Image processing apparatus, method and program for gradation conversion

1. An image processing apparatus comprising: first calculating means for adding a pixel value of an image and an output of filter means for performing filtering in space directions on a modulation error of a quantized value obtained by quantizing the pixel value of the image; first quantizing means for quantizing an output of the first calculating means and outputting a quantized value serving as ΔΣ modulation data, which is a result of ΔΣ modulation performed on the pixel value; second calculating means for calculating a difference between the output of the first calculating means and the output of the first quantizing means, thereby obtaining a quantization error; second quantizing means for quantizing a portion of the quantization error and outputting a quantized value obtained through the quantization, the quantized value serving as compensating data for compensating for error diffusion in space directions; dequantizing means for dequantizing the ΔΣ modulation data; third calculating means for adding the dequantized ΔΣ modulation data and the compensating data, thereby generating time-integration-effect-using error diffusion data that generates an effect of an error diffusion method using a visual integration effect in a time direction; fourth calculating means for calculating a difference between the quantization error and the compensating data, the difference serving as a ΔΣ modulation error, which is a quantization error used for the ΔΣ modulation; and the filter means for performing filtering in space directions on the ΔΣ modulation error.

2. The image processing apparatus according to claim 1 , wherein, in a case where the pixel value of the image is N bits and where the first quantizing means outputs a quantized value of M bits (M smaller than N) the ΔΣ modulation data, the dequantizing means dequantizes the ΔΣ modulation data into N bits; the second quantizing means quantizes the portion of the quantization error into N-M bits and outputs a quantized portion obtained thereby as N-M-bit compensating data, and the third calculating means adds the ΔΣ modulation data the third calculating means adds the N-bit dequantized ΔΣ modulation data and the N-M-bit compensating data, thereby generating N-bit time-integration-effect-using error diffusion data.

3. The image processing apparatus according to claim 2 , further comprising: frame rate control means for performing a converting process of converting the time-integration-effect-using error diffusion data of N bits into a pixel value of M bits by using a frame rate control process.

4. The image processing apparatus according to claim 1 , wherein filter coefficients of filtering performed by the filter means are determined so that an amplitude characteristic of noise shaping performed based on the ΔΣ modulation becomes a reverse characteristic of a human visual characteristic in a midrange and higher and that a gain in the amplitude characteristic increases in a high range more steeply compared to a gain in an amplitude characteristic of noise shaping performed based on ΔΣ modulation using a Floyd filter.

5. The image processing apparatus according to claim 1 , wherein filter coefficients of filtering performed by the filter means are determined so that a gain in an amplitude characteristic of noise shaping performed based on the ΔΣ modulation is negative in a low range or midrange and increases in a high range more steeply compared to a gain in an amplitude characteristic of noise shaping performed based on ΔΣ modulation using a Floyd filter.

6. The image processing apparatus according to claim 1 , wherein filter coefficients of filtering performed by the filter means include a negative value and are determined so that a gain in an amplitude characteristic of noise shaping performed based on the ΔΣ modulation increases in a high range more steeply compared to a gain in an amplitude characteristic of noise shaping performed based on ΔΣ modulation using a Floyd filter.

7. An image processing method for an image process apparatus including first calculating means for adding a pixel value of an image and an output of filter means for performing filtering in space directions on a modulation error of a quantized value obtained by quantizing the pixel value of the image; first quantizing means for quantizing an output of the first calculating means and outputting a quantized value serving as ΔΣ modulation data, which is a result of ΔΣ modulation performed on the pixel value; second calculating means for calculating a difference between the output of the first calculating means and the output of the first quantizing means, thereby obtaining a quantization error; second quantizing means for quantizing a portion of the quantization error and outputting a quantized value obtained through the quantization, the quantized value serving as compensating data for compensating for error diffusion in space directions; dequantizing means for dequantizing the ΔΣ modulation data; third calculating means for adding the dequantized ΔΣ modulation data and the compensating data, thereby generating time-integration-effect-using error diffusion data that generates an effect of an error diffusion method using a visual integration effect in a time direction; fourth calculating means for calculating a difference between the quantization error and the compensating data, the difference serving as a ΔΣ modulation error, which is a quantization error used for the ΔΣ modulation; and the filter means for performing filtering in space directions on the ΔΣ modulation error, the image processing method comprising the steps of: adding the pixel value of the image and the output of the filter means, the adding being performed by the first calculating means; quantizing the output of the first calculating means and outputting the quantized value including the quantization error, the quantized value serving as the ΔΣ modulation data, the quantizing and the outputting being performed by the first quantizing means; calculating the difference between the output of the first calculating means and the quantized value of the output of the first calculating means, thereby obtaining the quantization error, the calculating being performed by the second calculating means; quantizing the portion of the quantization error and outputting the compensating data, the quantizing and the outputting being performed by the second quantizing means; dequantizing the ΔΣ modulation data; adding the dequantized ΔΣ modulation data and the compensating data, thereby generating the time-integration-effect-using error diffusion data, the adding being performed by the third calculating means; calculating the difference between the quantization error and the compensating data, the difference serving as the ΔΣ modulation error, the calculating being performed by the fourth calculating means; and performing filtering in space directions on the ΔΣ modulation error, the performing being performed by the filter means.

8. A non-transitory computer-readable medium having stored thereon a computer-readable program causing a computer to carry out the following steps first calculating step for adding a pixel value of an image and an output of filter step for performing filtering in space directions on a modulation error of a quantized value obtained by quantizing the pixel value of the image; first quantizing step for quantizing an output of the first calculating step and outputting a quantized value serving as ΔΣ modulation data, which is a result of ΔΣ modulation performed on the pixel value; second calculating step for calculating a difference between the output of the first calculating step and the output of the first quantizing step, thereby obtaining a quantization error; second quantizing step for quantizing a portion of the quantization error and outputting a quantized value obtained through the quantization, the quantized value serving as compensating data for compensating for error diffusion in space directions; dequantizing means for dequantizing the ΔΣ modulation data; third calculating step for adding the dequantized ΔΣ modulation data and the compensating data, thereby generating time-integration-effect-using error diffusion data that generates an effect of an error diffusion method using a visual integration effect in a time direction; fourth calculating step for calculating a difference between the quantization error and the compensating data, the difference serving as a ΔΣ modulation error, which is a quantization error used for the ΔΣ modulation; and the filter step for performing filtering in space directions on the ΔΣ modulation error.

9. An image processing apparatus comprising: a first calculating unit configured to add a pixel value of an image and an output of a filter unit configured to perform filtering in space directions on a modulation error of a quantized value obtained by quantizing the pixel value of the image; a first quantizing unit configured to quantize an output of the first calculating unit and output a quantized value serving as ΔΣ modulation data, which is a result of ΔΣ modulation performed on the pixel value; a second calculating unit configured to calculate a difference between the output of the first calculating unit and the output of the first quantizing unit, thereby obtaining a quantization error; a second quantizing unit configured to quantize a portion of the quantization error and output a quantized value obtained through the quantization, the quantized value serving as compensating data for compensating for error diffusion in space directions; dequantizing means for dequantizing the ΔΣ modulation data; a third calculating unit configured to add the dequantized ΔΣ modulation data and the compensating data, thereby generating time-integration-effect-using error diffusion data that generates an effect of an error diffusion method using a visual integration effect in a time direction; a fourth calculating unit configured to calculate a difference between the quantization error and the compensating data, the difference serving as a ΔΣ modulation error, which is a quantization error used for the ΔΣ modulation; and the filter unit configured to perform filtering in space directions on the ΔΣ modulation error.